The present invention relates to an operation control method and operation control apparatus of a variable speed generator-motor. More particularly, the present invention relates to an operation control method and operation control apparatus of a variable speed generator-motor for improving stability in a case of performing operation control by a synchronous operation method at the time of starting or stopping pumping of the variable speed generator-motor.
In a variable speed pumping-storage power generation system including a variable speed generation-motor, when a relationship between an electric output of a generator and a motor output of a water wheel becomes unbalanced during the use of a variable speed operation method, a change in the rotation speed of the water wheel occurs and therefore, a change in a slip frequency (rotation speed) transiently occurs. For example, when the generator output is suddenly increased during a power-generating operation, the rotation speed of the water wheel is transiently lowered, whereas when the generator output is suddenly decreased, the rotation speed of the water wheel is transiently raised.
In order that the variable speed generator-motor may continue operating with stability, the variation range of a slip frequency is required to fall in a specified range (variable speed operation range). Therefore, for the purpose of preventing the slip frequency from deviating from the variable speed operation range, there is used a synchronous operation method for operating in a state where the slip frequency is held constant. This synchronous operation method is realized by fixing the slip frequency and a torque direction excitation current command value. However, when the variable speed generator-motor is started or stopped using the synchronous operation method, the excitation amount fails to be controlled to the optimum value to fix the torque direction excitation current command value, and therefore, an unstable phenomenon occurs due to over excitation or under excitation. As a result, when the synchronous operation method is used at the time of starting or stopping the pumping of the generator-motor, there is a problem that fluctuations of an effective power occur in a process where the effective power increases or decreases.
For the purpose of suppressing the above-described fluctuations of the effective power, a torque direction excitation current component of the variable speed generator-motor is adjusted and operated so as to reach a predetermined value.
In JP-A-08-80094, disclosed is an example of an operation control method using a method for calculating the optimum torque direction excitation current command target value of the excitation current from an effective power PL by a predetermined conversion formula (PL×C+D) (C and D are constant numbers) at the time of starting the pumping of the variable speed generator-motor and for adjusting a torque direction excitation current command value fixed immediately before switching to the synchronous operation method so as to approximate a target value calculated using the conversion formula, as well as using a method for raising or lowering the fixed torque direction excitation current command value up to a predetermined value previously set.